One of the biggest communication problems with respect to anthropogenic climate change is that for most people climate change is perceived as a threat in the future, and therefore most likely only future generations will feel the impacts. An exception to this fact are extreme weather events some of which are already being made more likely by climate change. If this causal connection can be drawn to public attention at the time, the impact of climate change could potentially be made more real and immediate in the public consciousness.

Shrewsbury Abbey from the west, November 2000, by Bob Bowyer, geograph.org.uk

Up until very recently, however only general statements about such events could be made which again did not help in getting the message across that climate change is not just a future problem. In a warming world particular types of weather events, such as heat waves and extreme rainfall, will become both more intense and more frequent with a rising mean global temperature. However, such general physical reasoning (e.g. warmer air can contain more water vapour leading to more intense and more frequent rainfall events) leaves us unable to say more than that such extreme weather events are consistent with climate change *.

Furthermore, the chaotic nature of weather means that it is generally impossible to say, for any specific event, that it would not have occurred in the absence of human influence on climate. In a simple analogy, a dice may be loaded to come up six, but a six could have come up anyway without the loading. Many people therefore think that it is impossible to attribute specific extreme weather events to past gas emissions, even in principle. However, this is not the case.

BAMS special report: Explaining Extreme Events of 2013 from a Climate Perspective

In the last decade a new field of research, probabilistic event attribution (PEA) has emerged, and developed the methodology to identify a human fingerprint in individual extreme weather events. The framework was introduced in 2003 by Myles Allen in Oxford and in 2004, Stott et al. published the first paper in Nature applying PEA and showing that climate change at least doubled the risk of the record-breaking European heat wave in the summer of 2003. Since then, advances in the field have prompted numerous studies, leading the Bulletin of the American Meteorological Society (BAMS) to dedicate an annual special issue to extreme event attribution for the past three years.

In the probabilistic approach, possible weather under the observed climate conditions (e.g. greenhouse gas concentration, sea surface temperatures, etc.) is simulated over and over again using state-of-the-art climate models and thus obtaining statistics of weather under these conditions. At the same time possible weather is simulated under equivalent natural forcings (solar, volcanoes, etc) but with pre-industrial values of greenhouse gas concentrations in the atmosphere, hence we simulate possible weather in a world without anthropogenic climate change.

How climate change will increase the probability of extreme weather, in particular heatwaves in Australia

Using the analogy above we roll the weather dice over and over again to obtain statistics of rolling a six. Anthropogenic climate change might have loaded the dice to increase or decrease the probability of coming up six. While we do know that for unloaded dice the probability of coming up 6 is one sixth we do not know the probabilities of extreme weather events in a world without climate change because we have never observed such a world. The approach, therefore, depends crucially on model simulations and on the model’s ability to reliably simulate the climate conditions generating the extreme weather event. So, while attributing changes in risk of extreme events, e.g. heat waves, to increasing anthropogenic greenhouse gas emissions can be done with confidence, the robustness of attribution studies of other extreme events must be assessed on a case-by-case basis.

This has been done with several successful assessments on the human influence on the probability of occurrence of extreme precipitation events (Pall et al., 2011, Christidis et al., 2013, Lott et al., 2013, Schaller et al., 2014). Every extreme weather event is caused by a combination of different factors so a case-by-case analysis is necessary. However, crucially, it is now possible, using PEA, to link individual extreme weather events to their individual causes, one of which could be anthropogenic greenhouse gas emissions.

For each of such attribution studies the possible outcome could be that human greenhouse gas emissions have increased the likelihood of the event, or decreased it or played no detectable role. A fourth possibility would be that our current generation of climate models is unable to reliably reproduce the event. Apart from events that fall in the latter category (e.g. tornados) PEA offers the chance, for the first time, to directly link individual weather events to anthropogenic climate change and thus to assess whether and to what extent climate change is already taking its toll. In other words, it enables us to give a quantitative estimate of how much anthropogenic climate change is costing us today.

This ability could potentially have a huge impact on climate change communication. Extreme events, in particular those that are not just rare from a meteorological perspective but also lead to societal and monetary damages and interrupt everyday life usually receive a very high level of public attention. If attribution studies show that a particular event was indeed made more likely due to anthropogenic climate change, i.e. anthropogenic climate change has increased the chance of the event occurring at this point in time, human induced climate change is transformed from something that is happening at some point in the future to a real threat in the here and now. Hence, PEA can make anthropogenic climate change immediately graspable and thus invaluable to communicate the topic to the public, the press and the politicians.

Currently, these studies are published well after public attention to the event has peaked. However, while the first study attributing a high precipitation event (Pall et al., 2011) to anthropogenic climate change took several years to complete, the annual Bulletins of the American Meteorological Society (Peterson et al., 2012, 2013 Herring et al., 2014) only require months to complete. By refining the methodology and crucially involving more scientists and research groups globally in event attribution, the science is advancing quickly and validation and event definition processes are now possible in very short time frames.

Because a deep understanding of the relevant meteorological processes for each single event is necessary it is difficult to foresee these procedures being automated. Through a new partnership between Climate Central, a non-profit organisation providing TV weather forecasters with climate information, the University of Oxford Environmental Change Institute and other academic partners this huge communication opportunity will be taken to the next level by building a modelling and communication framework that provides decision-makers, and in particular the public, with the means to make clear the quantitative connections between greenhouse gas emissions and extreme weather events in real-time.

Map from Climate Central showing how extreme precipitation events are on the rise

This fast turn around ensures that any communication opportunity will have maximum impact as an extreme event only remains topical while it is unfolding. By hearing the science as the public experience the event, they will really begin to fully understand climate change.

]]>http://www.climateprediction.net/extreme-weather-events-friederike-otto/feed/0EPSRC funded PhD in Mathematics at University of Exeterhttp://www.climateprediction.net/epsrc-funded-phd-in-mathematics-at-university-of-exeter/
http://www.climateprediction.net/epsrc-funded-phd-in-mathematics-at-university-of-exeter/#commentsTue, 20 Jan 2015 14:35:18 +0000http://www.climateprediction.net/?p=3891Disentangling the impact of land use on climate change with Big Data

Using the HYDRA project, this PhD project will look at the uncertainty in the climate system due to land use change on both global and local scales. This will make use of a very large (100,000+ experiments) model ensemble using the climateprediction.net distributed computing system.

]]>http://www.climateprediction.net/epsrc-funded-phd-in-mathematics-at-university-of-exeter/feed/0Website up and running againhttp://www.climateprediction.net/website-up-and-running-again/
http://www.climateprediction.net/website-up-and-running-again/#commentsTue, 06 Jan 2015 17:04:31 +0000http://www.climateprediction.net/?p=3872I’m pleased to let you know that the website is now up and running again, after being down over Christmas.

Sorry if this caused any inconvenience.

From everyone in the CPDN team, we hope you had a lovely Christmas and New Year!

]]>http://www.climateprediction.net/website-up-and-running-again/feed/0Europe’s Record Heat Directly Tied to Climate Changehttp://www.climateprediction.net/europes-record-heat-directly-tied-to-climate-change/
http://www.climateprediction.net/europes-record-heat-directly-tied-to-climate-change/#commentsThu, 18 Dec 2014 12:39:44 +0000http://www.climateprediction.net/?p=3859As 2014 comes to a close, Europe is virtually certain to lock in its hottest year in more than 500 years, and according to research by three independent teams of climate scientists, including climateprediction.net, the record can be closely attributed to climate change.

The three groups, from the UK, the Netherlands and Australia, each using a different method, found that Europe should best its previous heat record set in 2007, and that setting that record has been made at least 35 to 80 times more likely by the manmade rise of greenhouse gases in the atmosphere.

“All the groups are concluding there is a very substantial influence of human caused climate change on increasing the chances of setting a new record in 2014,” said David Karoly, an atmospheric scientist at the Australian National University and one of the project researchers.

Extreme heat events are one of the signature extremes expected in a warming world, according to climate model projections, be they a record hot summer in Australia or a record hot year for any part of the planet or the globe as a whole. And in general, the link between climate change and extreme heat is clearer and easier to discern than for other forms of extreme weather, such as extreme downpours or drought.

Different Methods, Same Conclusion

In this analysis of extreme heat, each team used different methodology and came up with slightly different numbers for the 2014 record projection and the likely role that climate change played, but all showed a heavy influence of manmade climate change on the recent heat records.

Globally, as well as in Europe, nine of the 10 hottest years ever recorded have all occurred since 2000. No annual cold record has been set in Europe since 1956 as warming is making hot years hotter and more frequent. No year has been record cold globally since 1911.

Of course, the world doesn’t warm uniformly. In the U.S., for example, the eastern part of the country has had a fairly cool year while parts of the West are on pace for record temperatures. And many other parts of the planet have been baking, including Europe.

Nineteen European countries are on track for their hottest year on record: Austria, Belgium, Croatia, Czech Republic, Denmark, France, Germany, Hungary, Iceland, Italy, Luxembourg, The Netherlands, Norway, Poland, Serbia, Slovakia, Slovenia, and the United Kingdom. Sweden is projected to tie its record high.

Oxford Experiment

Our team at the University of Oxford, led by Myles Allen and Friederike Otto, used thousands of iterations of regional climate models embedded within larger global models to examine more localized weather events.

For example, our data for Germany determined that what was once a 1 in 80-year heat event has now become a 1 in 7-year event, making it 10 times more likely due to global warming.

Using our volunteers’ computers for our weather@home project, we simulated possible European weather based on the observed global ocean temperatures. At the same time, we also simulated a 2014 where there is no human-influenced climate change. Comparing those two “worlds” we found that the 2014 European temperatures were much more likely in the world with climate change than the one without.

“It is important to highlight that Oxford’s result crucially depends on the 2014 global ocean temperatures. The same study using 2000-2011 conditions gives a different result although the anthropogenic warming is the roughly same in these years,” said Dr Friederike Otto.

“When looking at smaller regions in Europe, we notice that there is a higher variability of temperatures,” Karsten Haustein, who conducted the analysis, said. “For example, in central Europe we found that the probability of reaching the observed 2014 temperatures is about 40 times higher. In an even smaller region such as the UK, we found that the probability has increased by a factor of about 10.”

Research from the Netherlands

As a continent, Europe is set to break its record by 0.12°C, according to new estimates made by Geert Jan van Oldenborgh at KNMI, and explained in the Climate Indicator Bulletin released by the World Meteorological Organization’s Regional Climate Center for Europe and the Middle East.

Van Oldenborgh used both modern and early temperature records, as well as sources like tree rings, which can act as a proxy for very old temperatures, to observe Europe’s temperature records back to 1500 and determined that 2014 will almost certainly be the warmest year Europe has experienced during the past 500 years.

When looking at the record of temperatures over time, “you see that the world is getting warmer and hence Europe is getting warmer,” van Oldenborgh said.

Using those observational records, van Oldenborgh’s analysis concluded that global warming has made a temperature anomaly like the one observed in 2014 in Europe at least 80 times more likely.

At the beginning of the 20th century, before the global warming signal emerged from the noise of year-to-year variability, the chances of seeing a year as warm as this one were less than one in 10,000, van Oldenborgh said. “It would be almost impossible to reach these temperatures a century ago.”

Australian Research

An Australian team led by Karoly and Andrew King of the University of Melbourne answered a slightly different question, which was to ask how much more likely it was to break the 2007 record with warming than without. To do this they used the same model simulations used in the Intergovernmental Panel on Climate Change’s most recent report.

They found that the accumulation of greenhouse gases, which increases the chances of a record warm year every year they accumulate, made such an event 35 times more likely.

Similar Results

The differences in the numbers calculated by each group are a product of the slightly different questions each team asked, as well as the inherent uncertainty in these sorts of measurements, given how rare extreme events are, van Oldenborgh said. But for this heat event, “these numbers are very close given the uncertainties,” he said. That agreement across studies “gives us confidence in the result that global warming made a temperature this high in Europe much more likely.”

The results are also in line with previous work of Karoly’s that found that the record warm year Australia experienced in 2013 was “virtually impossible” without the influence of global warming, as he put it.

“What we’ve been finding is that there’s a very clear signal on human influences on increases in the likelihoods of record temperatures,” Karoly said.

This article is an edited version of articles that appeared on the Climate Central website – read the originals here and here.

]]>http://www.climateprediction.net/europes-record-heat-directly-tied-to-climate-change/feed/0New publication on the experimental setup of weather@homehttp://www.climateprediction.net/new-publication-on-the-experimental-setup-of-weatherhome/
http://www.climateprediction.net/new-publication-on-the-experimental-setup-of-weatherhome/#commentsThu, 30 Oct 2014 11:48:24 +0000http://www.climateprediction.net/?p=3721A paper detailing the model development, experimental setup and validation of the weather@home project has been published in the Quarterly Journal of the Royal Meteorological Society.

The paper explains the background to climateprediction.net and how the project is using regional climate modelling to answer questions about the attribution of extreme weather events – “Was the event caused by anthropogenic climate change?”

weather@home – development and validation of a very large ensemble modelling system for probabilistic event attribution

]]>http://www.climateprediction.net/new-publication-on-the-experimental-setup-of-weatherhome/feed/0New publication about extreme summer rainfall in England and Waleshttp://www.climateprediction.net/new-publication-about-extreme-summer-rainfall-in-england-and-wales/
http://www.climateprediction.net/new-publication-about-extreme-summer-rainfall-in-england-and-wales/#commentsTue, 14 Oct 2014 14:38:38 +0000http://www.climateprediction.net/?p=3669A new publication by our Science Coordinator, Dr Friederike Otto, has been published in Climatic Change about our recent research into extreme summer rainfall events in England and Wales as an example for probabilistic event attribution.

In the summer of 2007 England and Wales experienced very heavy flooding. Summer precipitation and subsequently flooding are harder to model than winter or autumn rainfall and this recent publication highlights this again. We look at different possible drivers of high precipitation in summer and do not find a conclusive signal apart for the July precipitation which might have been exacerbated due to anthropogenic forcing. However, the focus of the paper is not so much the attribution of the extreme precipitation to external climate drivers but the quantification of the uncertainties involved in such a study. The paper is part of a special issue dedicated to exactly these issues which will soon be published in full.

“This lecture provides an overview of the climate change issue, highlighting what are, in my view, the most important findings of the latest IPCC report and their implications for climate negotiations under the United Nations Framework Convention on Climate Change (UNFCCC). We will focus on three numbers that matter a lot, and mention along the way some other numbers that matter rather less than you might think.

The first important number is 95%, the level of confidence the climate science community now has that human influence is the dominant cause of the warming observed over the past 60 years. I will explain where this number comes from, with a quick (and colourful) introduction to the methods used for “detection and attribution” in the IPCC Working Group I report, and explain why the apparent “pause” in ocean surface warming over the past decade or so doesn’t really change the big picture.

The second important number is 40.3 degrees C (105 degrees F), the national average temperature high over Australia on January 7th, 2013. While bad enough for Australia, the significance of that “Angry Summer” for the rest of the world is as an example of the kind of damaging weather event that, subsequent studies have shown, was made substantially more probable by human influence on climate. With the IPCC Working Group II finding that the impacts of climate change on human and natural systems are now evident on all continents and across the oceans, understanding the links between climate change and harmful weather events is becoming important for the UNFCCC’s new “Loss and Damage” agenda, and a key focus of Oxford’s climateprediction.net/weatherathome project.

The third number is the big one: one trillion tonnes. That is the total amount of fossil carbon that the IPCC estimates can be dumped into the atmosphere over the entire Anthropocene epoch while keeping the resulting warming to likely less than two degrees Celcius. Over half a trillion tonnes has already been emitted, and accounting for warming due to other forms of pollution cuts down the remaining “carbon budget” further still. This puts the mitigation challenge into perspective, and helps explain why the IPCC Working Group III report found such a pivotal role for carbon capture and storage in scenarios that have some chance of meeting the two degree goal.

What are the numbers that matter less than you might think? One of them, although much tweeted, is “97% of scientists agree…” I’ll explain how this kind of opinion poll isn’t really relevant to how science, or the IPCC, actually works. Another over-rated number is the Equilibrium Climate Sensitivity (the subject of earlier climateprediction.net experiments), which turns out to matter much less than people thought. Finally, if you are hoping for a purely scientific argument that two degrees is the threshold for dangerous anthropogenic interference in the climate system, you will be disappointed: the IPCC reports make it clear that the assessment of what is dangerous has an ethical and moral dimension and cannot be resolved by any purely technical assessment.”

]]>http://www.climateprediction.net/live-stream-ipcc-ar5-three-numbers-that-matter-and-numbers-that-matter-less-than-you-think/feed/0Explaining Extreme Weather Events of 2013 from a Climate Perspectivehttp://www.climateprediction.net/explaining-extreme-weather-events-of-2013-from-a-climate-perspective/
http://www.climateprediction.net/explaining-extreme-weather-events-of-2013-from-a-climate-perspective/#commentsMon, 29 Sep 2014 15:28:59 +0000http://www.climateprediction.net/?p=3616The annual Bulletin of the American Meteorological Society (BAMS) special issue on the attribution of last year’s extreme weather events is published today. This year’s issue “explaining extreme events of 2013 – from a climate perspective” includes two papers led by researchers from our climateprediction.net team.

This is a highly-cited and influential annual publication coined in 2012 asking whether and to what extent anthropogenic climate change altered the risk of major extreme weather events of the past year to occur.

The first of these papers, led by Dr Nathalie Schaller, looked at the heavy rainfall last summer in the Upper Danube and Elbe Basins in central Germany.

Nathalie explains her research: “Using the weather@home project, we performed two types of experiments to investigate the effect of human influence on the heavy precipitation event that occurred in May-June 2013 in Central Europe and led to floods along the Elbe and Danube rivers. Comparing extreme rainfall amounts in the Elbe and Danube catchments in simulations of the ‘world as it happened’ and of the ‘world that might have been’ shows that human influence did not affect the risk of such an event happening.

An attribution study that was based only on observations came to the same conclusion. This paper shows that despite the fact that in a warming world we do expect and observe more extreme precipitation on average, this is not true for all regions and all types of events.”

The second paper, by Dr Juan Añel Cabanelas and colleagues, looked at the extreme snow in the western Spanish Pyrenees during the winter and spring of 2013.

Juan explains his research: “We analyzed a phenomenon of extreme snow accumulation in the Pyrenees for several months of 2013 using different techniques. The phenomenon was extreme and rare. However results from weather@Home simulations were not able to find a conclusive fingerprint of climate change on it. If anything, the results suggest a slight decrease of the likelihood of such an accumulation of snow occurring in a warming world but this decrease is not scientifically significant.”

The special issue comprises of 22 studies of 16 events that occurred in 2013 all over the world. A particular focus of 5 studies was the extreme heat in Australia, which forced the local meteorological services to design a new colour for the weather maps to display unprecedented heat. All found a strong increase in the risk of such record-breaking heat waves occurring in a warming world, with Knutson et al. showing that the annual mean temperatures in Australia in 2013 are impossible to simulate without global warming.

The studies of extreme precipitation and cyclones show that our understanding of how the probability of their occurrence changes in a warming world is less complete, however, as the report concludes, a “failure to find anthropogenic signals for several events examined in this report does not prove anthropogenic climate change had no role to play. Rather, an anthropogenic contribution to these events that is distinguishable from natural climate variability could not be detected by these analyses. Thus, there may have been an anthropogenic role, but these particular analyses did not find one.”

In compiling different methods to answer the same research question and highlighting the strengths and weaknesses in these methods and gaps in our understanding these annual reports add considerably to the body of evidence of climate change.

Download the full report from the American Meteorological Society website.